The present invention relates generally to computer data base searching, and more particularly to searching through a distributed database.
It was known to aggregate data in advance to facilitate searches. Data aggregation can be performed as a batch process. However, this causes a time delay before new data can be searched. Furthermore, reconstruction of a database may be required when adding a new data item.
It was also known to create a distributed or federated database for managing scattered data. For example, see L. M. Haas et al., “DiscoveryLink: A system for integrated access to life sciences data sources”, IBM Systems Journal Vol. 40, No. 2, 2001; and “DB2 Information Integrator V8” (technical paper) (IBM Systems Journal Vol. 41)”, 2002, IBM Japan, retrieved on Aug. 27, 2003 via the Internet <URL: http://www-6.ibm.com/jp/software/data/developer/library/techdoc/d b2func.html#ii>. This is a technique for providing an integrated database image from a distributed database by directly accessing the distributed database. The distributed databases are not aggregated, which avoids a delay in searching for new data. Furthermore, due to the direct access of the individual databases, it is easier to add new data.
FIG. 14 illustrates a prior art integrated search by a distributed database system 1410. Distributed database system 1410 performs an integrated search using a single search expression (SQL: Structured Query Language) for each of the tables of databases 1421 in multiple servers 1420 to obtain a single image as the search result. Thus, the distributed database in the multiple servers 1420 can be searched as a single database.
As described above, by using a distributed database system, it is possible to directly access individual databases to perform data searches, without aggregating the data. In a distributed database system, however, a search similar to an ordinary database search may be performed using a search expression in SQL. With this type of search, a response is not received until the search has been finished and the search results are obtained. The time required for the search cannot be accurately predicted before the search ends. Furthermore, in the distributed database system, a search is performed with a single SQL search expression. Due to the characteristics of SQL systems, the search process cannot be interrupted once started until all the target databases have been searched. Therefore, flexible operations cannot be performed during the search, such as checking the progress status, canceling the search, and changing the search condition to resume the search.
Accordingly, an object of the present invention is to enable flexible operations during execution of a search, such as checking the progress status, predicting the time required for the search and permitting an interrupt by other processes, in a distributed database system.